Method and apparatus for steam dealkylation in a plant for the catalytic splitting of hydrocarbons

ABSTRACT

A method and apparatus for treating a fraction consisting predominantly of hydrocarbons having at least seven carbon atoms (C 7+  fraction) as produced in a plant for the catalytic splitting of hydrocarbon-containing feedstock, is disclosed. Following hydration, the C 7+  fraction is taken to steam dealkylation where the usable products benzene and hydrogen are produced.

This application claims the priority of German Patent Document No. 102006 038 891.7, filed Aug. 18, 2006, the disclosure of which isexpressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method for treating a fraction consistingpredominantly of hydrocarbons having at least seven carbon atoms (C₇₊fraction) as produced in a plant for the catalytic splitting ofhydrocarbon-containing feedstock and an apparatus for carrying out themethod.

Primarily heavy crude oil components such as are produced, for example,in crude oil distillation are processed in a plant for the catalyticsplitting of hydrocarbon-containing feedstock.

In accordance with the prior art, the heavy crude oil components aretaken as feedstock for catalytic splitting. In catalytic splitting inthe presence of a catalyst, the heavy crude oil components are convertedprimarily into shorter-chain paraffins, olefins and aromatics. Afraction consisting predominantly of hydrocarbons having at least sixcarbon atoms (C₆₊ fraction) is separated from the reaction products fromthe catalytic splitting. This C₆₊ fraction contains aromatics, primarilybenzene, as an economically utilizable product, which find a use asstarting material for the synthesis of numerous plastic materials and toincrease the knock resistance of gasoline.

In order to obtain the economically utilizable products from the C₆₊fraction, primarily benzene, and to maximize the yield as much aspossible, the following method is applied from the prior art. The C₆₊fraction is separated into a fraction consisting predominantly ofhydrocarbons having six carbon atoms (C₆₊ fraction) and a fractionconsisting predominantly of hydrocarbons having at least seven carbonatoms (C₇₊ fraction). The economically utilizable product benzene can beseparated directly from the C₆₊ fraction. The linear hydrocarbons areseparated from the C₇₊ fraction by means of fluid-fluid extraction andprocessed further as a raffinate, for example, the raffinate can bereturned to the feedstock for catalytic splitting. The C₇₊ fractionfreed from the linear hydrocarbons now contains primarily aromaticshaving seven to eight carbon atoms and is separated into a fractionconsisting predominantly of hydrocarbons having seven carbon atoms(mainly toluene) and into a fraction consisting predominantly ofhydrocarbons having at least eight carbon atoms (primarily xylene). Thefraction consisting predominantly of hydrocarbons having eight carbonatoms is taken as feedstock to a process for extracting paraxylene. Thefraction consisting predominantly of hydrocarbons having seven carbonatoms is taken as feedstock to a process for hydro-dealkylation.

A process of this kind for hydro-dealkylation is described, for example,in WO2005071045. The hydrocarbons are contacted with hydrogen in thepresence of a catalyst at a temperature of 400° C. to 650° C. and apressure between 20 bar and 40 bar, where the hydrogen is present in amolar excess of three to six times the hydrocarbons. Under theseconditions the alkyl groups are split off from the alkylated aromatics(such as toluene) so that benzene and the particular alkanes form(methane for example).

The consumption of hydrogen in the hydro-dealkylation of thehydrocarbons has a negative effect on the economics of this process fromthe prior art for extracting benzene.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates an embodiment of an apparatus in accordance with theprinciples of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In accordance with the invention, with respect to the method, the C₇₊fraction is subjected to steam dealkylation where mainly the twoutilizable products benzene and hydrogen are produced along withreaction products such as carbon monoxide and carbon dioxide.

The basic idea of the invention is to carry out dealkylation of thealkylated aromatics while generating benzene with the aid of steamdealkylation. Steam dealkylation requires only inexpensive steam as thestarting material and produces the valuable by-product hydrogen inaddition to the desired quality product benzene.

The C₇₊ fraction employed in the steam dealkylation contains primarily:

a) aromatic hydrocarbons having seven to ten carbon atoms,

b) cyclic paraffins (cycloalkanes) having six to ten carbon atoms,

c) iso- and n-paraffins having six to ten carbon atoms,

d) alkenes having seven to ten carbon atoms, or

any mixture of the aforementioned, where the precise composition isdependent on the composition of the specific heavier naphtha which istaken as feedstock for catalytic reforming. The inventive method issuitable for each of the compounds of the C₇₊ fraction described.

The hydrocarbons from the C₇₊ fraction react advantageously with steamin the gas phase with the introduction of heat to a solid catalyst. Thegaseous C₇₊ fraction is dealkylated by the presence of gaseous water(steam) on a catalyst under the constant introduction of heat, wherebythe desired products benzene and hydrogen are produced in addition tocarbon monoxide, carbon dioxide and additional by-products.

Preferably the heat required for the dealkylation reaction is generatedby the combustion of a starting material with air. It proves to beparticularly advantageous to use gaseous by-products from the steamdealkylation, specifically carbon monoxide and methane, as startingmaterial for combustion with air. A part of the gaseous reactionproducts from the steam dealkylation, in particular carbon monoxide andmethane, is combustible and can therefore serve as starting material forcombustion to generate the necessary reaction heat. This saves heatinggas and this otherwise unused part of the reaction products is employedusefully.

Following compression, the gaseous reaction products are expedientlyseparated by way of pressure swing adsorption into gaseous hydrogen andgaseous reaction by-products, specifically carbon monoxide, carbondioxide and methane. The valuable by-product hydrogen is also present ingaseous form and can be employed much more usefully than for combustion.By way of pressure swing adsorption preceded by compression, thehydrogen can easily be separated from the combustible gaseous reactionby-products which can serve as starting material in the combustion.

The flue gases generated in combustion are advantageously cooled via aheat exchanger while heating the starting materials for the steamdealkylation. By using the heat from the flue gases to preheat thestarting materials (C₇₊ fraction and steam) for the steam deakylation,the heat to be supplied which is needed to maintain the temperaturesrequired for the dealkylation reaction is reduced. This achieves aneconomical use of energy resources.

The C₇₊ fraction and the steam are advantageously conducted past thesolid catalyst, preferably in pipes from top to bottom, where thecatalyst is in the interior of the pipes. Heat is expediently suppliedto the pipes from the outside. The heat required for the dealkylationreaction is preferably transferred to the pipe by electromagneticradiation, thermal radiation and/or convection. The actual dealkylationreaction takes place in the interior of the pipe where the catalyst islocated. The two components of the reaction (C₇₊ fraction and steam) aretaken from top to bottom through the pipes filled with the catalyst. Theheat needed for the dealkylation reaction is generated outside the pipesand transferred by the mechanisms named to the pipe from which the heatreaches the inside of the pipes, the site of the reaction, by means ofthermal conduction and convection.

A solid catalyst of a porous carrier material is preferably used,specifically γ-Al₂O₃, MgAl spinel and/or Cr₂O₃, and an active componenton the surface of the carrier material, in particular Rh with 0.1-1.0%loading by weight and/or Pd with 0.2-2.0% loading by weight.

The steam dealkylation is advantageously performed at a temperature of400° C. to 600° C., preferably 450° C. to 550° C., particularlypreferably 480° C. to 520° C. and at a pressure of 1 to 15 bar,preferably 1.2 to 10 bar, particularly preferably 1.5 to 8 bar.

Steam dealkylation is expediently performed at a molar quotient of steamto hydrocarbons which lies in the range of 1 to 20, preferably from 2 to15, when it enters the reactor. In another embodiment of the invention,steam dealkylation is performed at a molar quotient of steam tohydrocarbons which lies in the range from 3 to 12, preferably from 5 to10, when it enters the reactor. Steam dealkylation is generallyperformed with a molar excess of water, where the exact ratio in thedifferent embodiments of the invention depends on the precisecomposition of the C₇₊ fraction.

It proves advantageous to subject the C₇₊ fraction to a process toconvert dienes and styrenes before steam dealkylation, wherespecifically hydrating methods are employed involving the consumption ofhydrogen. It is similarly advantageous to subject the C₇₊ fraction to aprocess to convert and remove components containing sulfur, nitrogenand/or oxygen before steam dealkylation, where specifically methods arealso employed involving the consumption of hydrogen. By employing thehydrating processes, the diolefins present in the C₇₊ fraction areconverted into their corresponding olefins, just as componentscontaining sulfur, nitrogen and oxygen can be converted and removed.Deactivation of the catalyst is reduced and the life of the catalyst isclearly increased.

The reaction products from the steam dealkylation are preferably cooledand separated in a 3-phase separation into gaseous reaction products,hydrocarbons and water. The reaction products coming from the steamdealkyation contain not only the desired quality products benzene andhydrogen but also reaction products such as carbon monoxide and carbondioxide and reaction by-products. To obtain the desired qualityproducts, the reaction products must be separated. This is done by wayof a 3-phase separation of the cooled reaction products into the gaseousreaction products, specifically hydrogen, carbon monoxide, carbondioxide and methane, into the hydrocarbons, specifically benzene, andinto water.

The hydrogen generated in the steam dealkylation of the C₇₊ fraction isexpediently fed completely or partially into the starting material forthe hydrogen-consuming processes. The hydrogen generated in steamdealkylation can be used entirely or partially for thehydrogen-consuming processes described in the previous section so thatthe need for hydrogen to be supplied externally is minimized.

In one embodiment of the invention, the hydrogen produced in the steamdealkylation of the C₇₊ fraction is taken as starting material to anyprocess consuming hydrogen, preferably to a process in the oil refineryfor converting and removing sulfur-containing components or a processfor splitting hydrocarbon-containing starting material by means ofhydrogen.

For a good yield of the desired reaction product benzene fromsteam-dealkylation, the reduction of the sulfur content in the C₇₊fraction prior to steam dealkylation to below 10 ppm, preferably below 3ppm, particularly preferably below 1 ppm proves advantageous.

Preferably the benzene is separated from the hydrocarbons of thereaction products through rectification. Following rectification, thebenzene advantageously undergoes adsorptive fine cleaning to dry andremove the trace components, where the benzene is directed across anadsorbent on which the trace components, as opposed to benzene, areadsorbed. By applying the inventive method, the benzene can be extractedfrom the reaction products by simple rectification and processed furtheror marketed. Expensive extraction or extractive rectification as whenapplying a process in accordance with the prior art is not necessary,thus reducing investment and process costs.

Components in the C₇₊ fraction boiling close to benzene or formingazeotropes are advantageously converted by steam dealkylation. Allheavier boiling reaction products than benzene from rectification,consisting predominantly of non-converted feedstocks from the steamdealkylation, are expediently returned to steam dealkylation as startingmaterial by way of optional hydration. In another embodiment of theinvention, all heavier boiling reaction products than benzene fromrectification, consisting predominantly of non-converted feedstocks fromsteam dealkylation are returned for hydration of the C₇₊ fraction, C₆₊fraction or for hydration of a fraction consisting predominantly ofhydrocarbons with at least five carbon atoms prior to steamdealkylation. By returning the non-converted feedstocks for hydration orfor steam dealkylation, circulation is achieved without losing valuablefeedstocks.

In another embodiment of the invention, a fraction consistingpredominantly of hydrocarbons having at least eight carbon atoms (C₈₊fraction) is separated through distillation from the C₇₊ fraction, wherethe separated C₈₊ fraction is taken as feedstock to a process forextracting paraxylene or for processing as gasoline.

Concerning the apparatus, the object is achieved by the apparatuscomprising an oven 100 with a furnace 110 and pipes 120 located in thefurnace. The actual steam dealkylation takes place in the pipes which inturn are located in the furnace of the oven where the heat required forthe dealkylation reaction can be generated.

The pipes are advantageously installed vertically in the furnace andhave heat expansion compensating elements 130 at the lower and/or upperend. The heat expansion compensating elements at the lower and/or upperend of the vertical pipes prevent mechanical stress from temperaturedifferences which can lead to increased wear of the pipes.

Each pipe expediently has a supply for the C₇₊ fraction and the steam,122, 124, respectively, and an outlet 126 for the reaction products.

It proves equally advantageous that each pipe is filled on the insidewith a catalyst 128, where the catalyst consists of a porous carriermaterial, in particular γ-Al₂O₃, MgAl spinel and/or Cr₂O₃ and an activecomponent on the surface of the carrier material, in particular Rh with0.1-1.0% loading by weight and/or Pd with 0.2.-2.0% loading by weight.

Preferably the oven has at least one burner 102 on the wall, the ceilingand/or the floor. The pipes are expediently suitable for an internalpressure of 1 to 15 bar, preferably 1.2 to 10 bar, particularlypreferably 1.5 to 8 bar, and for use in an oven with flame temperaturesof up to 1400° C.

The present invention is successful specifically in creating aneconomical alternative to the prior art for treating a C₇₊ fraction in aplant for the catalytic splitting of hydrocarbon-containing feedstock.Through the application of the inventive method and the inventiveapparatus, the valuable by-product hydrogen is generated in addition tothe usable product benzene.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A method for treating a fraction consisting predominantly ofhydrocarbons having at least seven carbon atoms (C₇₊ fraction) asproduced in a plant for catalytic splitting of hydrocarbon-containingfeedstock, wherein the C₇₊ fraction undergoes steam dealkylation, wheretwo useable product materials benzene and hydrogen are produced inaddition to reaction products such as carbon monoxide and carbondioxide.
 2. The method according to claim 1, wherein the C₇₊ fractioncontains: a) aromatic hydrocarbons having seven to ten carbon atoms; b)cyclic paraffins (cycloalkenes) having six to ten carbon atoms; c) iso-and n-paraffins having six to ten carbon atoms; d) alkenes having sevento ten carbon atoms; or any mixture of the aforementioned.
 3. The methodaccording to claim 1, wherein the hydrocarbons from the C₇₊ fractionreact with water in a gas phase with addition of heat to a solidcatalyst.
 4. The method according to claim 1, wherein heat required forthe dealkylation reaction is generated by combustion of a startingmaterial with air.
 5. The method according to claim 1, wherein gaseousreaction products from the steam dealkylation are separated followingcompression by way of pressure swing adsorption into gaseous hydrogenand gaseous reaction by-products, specifically carbon monoxide, carbondioxide and methane.
 6. The method according to claim 5, wherein thegaseous reaction by-products from the steam dealkylation, specificallycarbon monoxide and methane, are used as starting material for thecombustion with air.
 7. The method according to claim 1, wherein fluegases generated during combustion are cooled by a heat exchanger whileheating starting materials for the steam dealkylation.
 8. The methodaccording to claim 1, wherein the C₇₊ fraction and the steam areconducted in pipes, from top to bottom, past a solid catalyst, where thecatalyst is on an inside of the pipes.
 9. The method according to claim8, wherein heat is brought to the pipes from outside.
 10. The methodaccording to claim 9, wherein the heat required for the dealkylationreaction is transferred to the pipes by electromagnetic radiation,thermal radiation and/or convection.
 11. The method according to claim1, wherein a solid catalyst of a porous carrier material is used,specifically γ-Al₂O₃, MgAl spinel and/or Cr₂O₃ and an active componenton a surface of the carrier material, in particular Rh with 0.1-1.0%loading by weight and/or Pd with 0.2.-2.0% loading by weight.
 12. Themethod according to claim 1, wherein the steam dealkylation is performedat a temperature of 400° C. to 600° C., preferably 450° C. to 550° C.,particularly preferably 480° C. to 520° C.
 13. The method according toclaim 1, wherein the steam dealkylation is performed at a pressure from1 to 15 bar, preferably 1.2 to 10 bar, particularly preferably 1.5 to 8bar.
 14. The method according to claim 1, wherein the steam dealkylationis performed at a molar quotient of steam to hydrocarbons in a rangefrom 1 to 20, preferably from 2 to 15, when it enters a reactor.
 15. Themethod according to claim 1, wherein the steam dealkylation is performedat a molar quotient of steam to hydrocarbons which is in a range from 3to 12, preferably from 5 to 10, when it enters a reactor.
 16. The methodaccording to claim 1, wherein the C₇₊ fraction undergoes a process priorto the steam dealkylation to convert dienes and styrenes where inparticular hydrating methods are employed involving consumption ofhydrogen.
 17. The method according to claim 1, wherein the C₇₊ fractionundergoes a process prior to the steam dealkylation to convert and toremove components containing sulfur, nitrogen and/or oxygen, in whichspecifically hydrating processes involving consumption of hydrogen areemployed.
 18. The method according to claim 1, wherein the reactionproducts from the steam dealkylation are cooled and separated intogaseous reaction products, hydrocarbons and water in a 3-phaseseparation.
 19. The method according to claim 16, wherein the hydrogenproduced in the steam dealkylation of the C₇₊ fraction is fed completelyor partially into a starting material for the processes involving theconsumption of hydrogen.
 20. The method according to claim 17, whereinthe hydrogen produced in the steam dealkylation of the C₇₊ fraction isfed completely or partially into a starting material for the processesinvolving the consumption of hydrogen.
 21. The method according to claim1, wherein the hydrogen produced in the steam dealkylation of the C₇₊fraction is fed as starting material to a process consuming hydrogen inan oil refinery, preferably into a process to convert and removecomponents containing sulfur or a process to splithydrocarbon-containing starting material via hydrogen.
 22. The methodaccording to claim 1, wherein a sulfur content in the C₇₊ fraction isreduced to below 10 ppm, preferably below 3 ppm, particularly preferablybelow 1 ppm prior to the steam dealkylation.
 23. The method according toclaim 1, wherein the benzene is separated from the hydrocarbons by wayof rectification of the reaction products.
 24. The method according toclaim 23, wherein the benzene undergoes adsorptive fine cleaningfollowing rectification to dry and remove trace components, where thebenzene is passed across an adsorbent on which the trace components areadsorbed.
 25. The method according to claim 1, wherein componentsboiling close to benzene or forming azeotropes in the C₇₊ fraction areconverted by steam dealkylation.
 26. The method according to claim 23,wherein all heavier boiling reaction products than benzene fromrectification, consisting predominantly of non-converted feedstocks fromthe steam dealkylation are returned to the steam dealkylation asfeedstock via optional hydration.
 27. The method according to claim 23,wherein all heavier boiling reaction products than benzene fromrectification consisting predominantly of non-converted feedstocks fromthe steam dealkylation are returned prior to steam dealkylation forhydration of the C₇₊ fraction, a C₆₊ fraction or for hydration of afraction consisting predominantly of hydrocarbons having at least fivecarbon atoms.
 28. The method according to claim 1, wherein prior tosteam dealkylation a fraction consisting predominantly of hydrocarbonshaving at least eight carbon atoms (C₈₊ fraction) is separated throughdistillation from the C₇₊ fraction as feedstock, where the separated C₈₊fraction is taken as feedstock to a process to extract paraxylene or istaken for processing as gasoline.
 29. An apparatus for treating afraction consisting predominantly of hydrocarbons having at least sevencarbon atoms (C₇₊ fraction) as produced in a plant for catalyticsplitting of hydrocarbon-containing starting material wherein theapparatus includes an oven with a furnace and pipes located in thefurnace.
 30. The apparatus according to claim 29, wherein the pipes aremounted vertically in the furnace and have heat expansion compensatingelements at a lower and/or an upper end.
 31. The apparatus according toclaim 29, wherein each pipe has a supply for the C₇₊ fraction and thesteam and an outlet for the reaction products.
 32. The apparatusaccording to claim 29, wherein each pipe is filled on an inside with acatalyst, where the catalyst consists of a porous carrier material,specifically γ-Al₂O₃, MgAl spinel and/or Cr₂O₃ and an active componenton a surface of the carrier material, in particular Rh with 0.1-1.0%loading by weight and/or Pd with 0.2.-2.0% loading by weight.
 33. Theapparatus according to claim 29, wherein the oven has at least oneburner on a wall, a ceiling and/or a floor.
 34. The apparatus accordingto claim 29, wherein the pipes are suitable for an internal pressure of1 to 15 bar, preferably 1.2 to 10 bar, particularly preferably 1.5 to 8bar, and for use in an oven with flame temperatures of up to 1400° C.35. A method of extracting benzene from a hydrocarbon having at leastseven carbon atoms, comprising the steps of: producing the hydrocarbonhaving at least seven carbon atoms in a plant for catalytic splitting ofhydrocarbon-containing feedstock; subjecting the hydrocarbon having atleast seven carbon atoms to steam dealkylation; and producing benzenefrom the steam dealkylation.
 36. The method according to claim 35,further comprising the step of producing hydrogen from the steamdealkylation.